Process of fractionation and apparatus therefor



June 24, 193).`

w. K. A I Ewlsl PROCESS OF FRACTIONATION AND APPARATUSTHEREFOR FiledJan. 12. 1925 Tn/mmtoz Patented June 24, 1930 UNITED STATES PATENTOFFICE WARREN K. LEWIS, OF NEWTON, MASSACHUSETTS, ASSIGNOR T STANDARDOIL DEVELOPMENT COMPANY, A CORPORATION OF DELAWARE PROCESS OFFRACTIONATION AND APPARATUS THEREFOB Applicationv led January 12, 1925.Serial No. 1,781.

This inventionrelates to improvements in processes and apparatus forcracking hydrocarbon oil and fractionating the resulting product. Theinvention will be fully understood from the following description, reference being made to the accompanying drawing, in which the single figureis adiagrammatic View of one suitable apparatus.

In the drawing, reference numeral 1 dew notes cracking means arranged ina. furnace setting 2. lVhile a single coil is illustrated, it will beunderstood that one or more coils, pressure stills, or other suitableapparatus may be used. The stock to be treated .is fed in through pipe8. The coil 1 discharges through pipe 4 into a heat-insulated drum 5, inwhich further cracking takes place. A pipe 6 is arranged to takeoff thecontents of drum 5 to separating means 7 such as a fractionating 'orrectifying tower. It is preferred to use a drum of the type de-vscribed, but the invention is not limited in this respect.

The upper part of the separating means 7 is ordinarily designed tofunction as a rectifying column. It may be provided with a partialcondenser, such as a coil 8, or the;

reflux may be obtained byv returning a part of the condensate from thefinal condenser, or otherwise. The reflux is drawn from the tower,preferably above the point at which the cracked material is introduced.A pan 9 and draw-oil pipe 10 are provided for this purpose withdefiecting plates to direct the condensate from coil 8 into the pan. Abell-cap column may be used with good results. AI prefer, however, toemploy some type of tower filling l1 and 12, as illustrated.

The cracked product ordinarily asses into the tower at substantially theull pressure and temperature of the cracking unit, except for thepressure drop incidentL to overcoming rictional resistance to flow. itis usually desirable to introduce the material into the tower at a pointabout onethird or one-fourth of the distance from the bottomy to thetop.

A stream of an aeriform fluid, preferably an inert gas or vapor, such asoxygen-free flue gas, producer gas, lscrubbed still gas,

' returned lto the moved' through line 23.

or the like, is introduced into the bottom of the tower through pipe 13yand suitable distributing means, such as a sprayhead 14. The gas orvapor strips low boiling hydrocarbonsl from the heavy residue or tarrefluxing down the lower section l2 of the v tower and collecting at itsbase. When an eicient tower arrangement is used, the quantity of gasrequired to strip the tar is relatively' small.

The stripping gas or vapor may be recycled or not,'as desired. In theinstallation shown,v gasoline vapors mixed with the stripping fluid aretaken off through line 15 to a condenser 16, `which discharges into acontainer 17. The liquid product is drawn olif through line 19 and partof the gas is distillation apparatus through line '20. Grasl isinitially introduced at 21 or other suitable location, and its pressureismaintained by pump y 22. Gases generated by the cracking process arereleased/from the drum 17 by line 21a. Tar may be continuously orintermittently re- The cycle stock may be received in a hot accumulatortank 24 and returned by pump 25 to coil 1 for further cracking. 1' Aparticular4 object of the invention is to obtain the effective removalof hydrocarbons having -a low or intermediate boiling point that tend tobe retained by the tar. The material discharged from drum 5 comprisesvapor and liqui portions, the liquid containing dissolved vapors ofnaphtha and gas oil which mu'st .be stripped from the heavy tarryresidue.` The vapor immediately rises into section 11 while the liquiddrops down on the filling material 'of section 12. The composition ofsaid liquid depends on the temperature andv pressure conditions.

volatile products in the tar will not be vaporized and the remainingliquid will be vlighter in gravity and will contain to'o large afraction of low boiling oils to be useful as fuel oil. For this reasonit has been impractical heretofore f to operate fractionating towersyunder high pressures, since volatilel products could not beAeffectively removed.

high pressure is held Ain -separator 7, the

The function of the gas admitted to the separator through sprayhead 14is to reduce the partial pressure of the volatile constitui ents in thevapors, thus allowing those fractions 4to distill from the heavy tar.By'this `means the se aration is accomplished.

In view of) this fact, I may operate at pressures above those at whichprior h drocarbon f ractionating apparatus can ordY- narily functionproperly. For example, I may maintain with advantage a pressure ofmorethan 200 lbs. per sq. in., say 250 lbs.' or more, on thefractionating apparatus orI separator and produce a tar substantiallfree from naphtha or light oils Whc could not be obtained under the highpressure without the use of gas.

An important feature of my invention is the provision of effective`countercurrent flow of the gas introduced and the tar bein stripped byit. In the apparatus illustrate this is accomplished by causing thevheavy c condensate to flow downwardly over the porphase,the inventionis: not limited in this respect.` The boil, drum, and condensing ouspacking 12 placed above the spray-head 14.. Merely injecting steam orgas into a body of heavy condensate will not accomplish the resultdesired.l

The pressure in the separator 7 will ordinarily approach or equal thatof the crack-p ing system for, althou h the temperature in 7 is lessthan in 5, t e gas-added at ,14 allows the vaporization of a large partof the material as liquid in 5. This has important advantages. Forexample, since the cycle stock is discharged under substantially `thefull pressure of the cracking unit, little eX- -pense in pumping isrequired for the return of this stock to coil 1. Also, its temperatureis materially higher when high pressure is maintained on Athedistillation means.

The extent to which the light fractions are removed from thetar'-may bereadilyv the a'mount of in regulated by adjustin ert gas introduced. Ithe tar tends to become too viscous for easy handling, the gas streamshould be'. reduced. The reflux through the tower may be re ated tosecure the .desired quality of al product. The feed stock, or othersuitable liquid, may be used as the cooling means in coil 8.

WhileI have illustrateda system inwhich means for returning said heavycondensate` to the-cracking coil.

. 2. Process of operating hydrocarbon cracking and fractionatingsystems, comprising conducting the cracking and fractionating operationsin separate zones under substantially the same pressure, in excess of200 lbs. per sq. in., such pressure in the fractionating operation beingin part maintained by vaporization and evolution of volatile productsfrom the stock treated, and in part by introduction of gas into thefractionating zone, under pressure from an external source in effectivecountercurrent relation to unvaporized stock, condensing heavy vaporizedproducts and separately collecting them in the -fractionating zone andreturning-the heavy condensate to the cracking system together with thefresh feed.

3. Process of operating hydrocarbon cracking and fractionating systems,comprising cracking hydrocarbons under superatmospheric pressure in acracking zone, fractionating the cracked products into tar, cycle stockand overhead distillate in a fractlonating zone under superatmosphericpressure not exceeding the pressure in the cracking zone, furtheringvaporization in the fractionating zone byintroducing inert'gas thereintoin effective counter current relatlon to Junvaporized cycle stock, andreturning the cycle stockto the crackingxzone for furtherdigestioncpf'che.- oil take-s place .in liquid system' may be operatedin various ways in connection with the utiliz ion of of rem lualcracking is allowed to take place in thnejlar-strippng apparatus. Thevfrac- -tionati'ng column maybe a part of the tar'- v as from 'o anextraneous source for maintaimng pres- "'sure. If desired, theinventionmay be applied in a' unit Vin which a certain amount 1

